1. Field of the Invention
The present invention relates to a thermal development apparatus for heating and developing photothermographic imaging material.
2. Description of Related Art
In a thermal development process for heating and developing a photothermographic imaging film (hereinafter, simply named xe2x80x9cfilmxe2x80x9d), as disclosed in Japanese Translation of PCT Patent Application (Tokuhyohei) No. H10-500497, a member obtained by coating a surface layer of a heating drum with an elastic member (silicon rubber) having heat resistance and high thermal conductivity has been put to practical use as a heating means for heating the film.
Particularly, in a thermal development unit for developing a silver salt photothermographic imaging film obtained by using the organic solvent, when the film is developed, a surface active agent of a surface layer of the film and/or the organic solvent or an organic acid of an emulsion layer are liberated from the film and attach to an elastic member (silicon rubber) forming the surface layer of the heating drum. Therefore, the elastic member (silicon rubber) deteriorates, and the swelling and abrasion of the elastic member (silicon rubber) is generated. Accordingly, a problem is arisen that the finished image having a stable quality cannot be obtained.
To solve the problem, in the Published Japanese Patent Application (Tokugan) No. 2002-208438, there is a technique of coating the surface layer made of the elastic member (silicon rubber) having the high thermal conductivity with fluororesin such as Teflon (trade name) to prevent the elastic member (silicon rubber) of the high thermal conductivity from being attacked by the surface active agent included in the surface layer of the film and/or the organic solvent or the organic acid of the emulsion layer in the developing of the film. This technique prevents the elastic member such as silicon rubber from gradually deteriorating with the elapsing of time. Accordingly, the finished image of the stable quality can be obtained.
However, when the surface of the elastic layer is coated with the fluororesin, though the lengthened life time of the heating drum and the lengthened cycle of the cleaning and maintenance of the heating drum can be achieved, there are following problems peculiar to the fluororesin.
(1) The carrying force caused by the low friction factor is insufficient.
(2) The development is made inactive because of the lowering of the thermal conductivity.
(3) The film is not tightly in contact with the drum in an axial direction of the drum, and a certain volume of air layer is generated between the film and the drum.
The problem (1) will be described hereinafter. As is well-known, Teflon (trade name) is the material having a low friction factor and is used as a sliding member. Therefore, when the nipping pressure of the opposed rollers arranged around the heating drum is set in the same condition as that in case of the heating drum with the elastic member of silicon rubber, the film carrying force during the thermal development drastically lowered, and there is a probability that the film slips on the drum. The slipping of the film causes the lengthening of the entire development period of time practically. This may cause a change in the density of the image, wrinkles or damage on the surface of the film.
The advance of the development of the photothermographic imaging film is determined by the product of the heating temperature and the heating time. Therefore, when the constant heating time, in other words, the constant film carrying speed is not maintained during the carrying from the top to the end of the film, the unevenness in the density of the image occurs. Therefore, in the thermal development apparatus having the heating drum with the surface layer made of the elastic member such as silicon rubber corresponding to the earlier art, to prevent the unevenness in the density of the image and the unevenness of wrinkles, the carrying speed in the thermal development unit and the carrying speeds on the upstream and downstream sides of the thermal development unit are set to the relation of (carrying speed on upstream side) less than (carrying speed in thermal development unit) less than (carrying speed on downstream side).
The problems (2) and (3) will be described hereinafter. The effective supplying of heat energy to the photothermographic imaging film, the obtaining of the finished image of the desired density and the suppression of the photographic fog on the film in the thermal development apparatus are achieved by thermally developing and carrying the film while pressing the film on the surface of the elastic member (silicon rubber) of the high thermal conductivity by the opposed rollers. However, because the thermal conductivity of Teflon (trade mark) is approximately one-third of that of the elastic member used in the earlier art, the inactiveness of the development occurs in the film when layer of Teflon is excessively thick, and the finished image having the desired density cannot be obtained.
Further, when the film is nipped between the opposed roller and the heating drum having the silicon rubber layer on its surface, even though the parallel relation between the heating drum and the opposed roller is not obtained in the axial direction of the heating drum in some degree of precision, the elastic layer of silicon rubber makes the film be able to uniformly and be tightly in contact with the heating drum and the opposed roller. On the other hand, in case of the existence of the surface layer coated with Teflon (trade mark), when the nipping pressure of the opposed roller and the parallelism are set in the same condition as those in the case of the heating drum with the silicon rubber, there is a probability that the film is not uniformly and tightly in contact with the heating drum and the opposed roller. Therefore, while considering the problem (1), it is important to optimize the biasing force of the opposed rollers and the alignment between the heating drum and each opposed roller, with more emphasis of the tight contact of the film with the heated surface than that in the earlier art.
Because the air layer is generated between the drum and the film due to the non-tight contact of the film with the drum in the axial direction of the drum, the heat transfer from the drum to the film further deteriorates in case of the coating of the drum with fluororesin, and the density in the final image is undesirably lowered. In case of the use of the drum coated with fluororesin, it was found out by the experiment of the inventors that there is/are a steep change(s) in the distribution of temperatures in the neighborhood of the surface of the drum, as compared with the case of the use of the drum coated with silicon rubber. Therefore, when the contact of the film with the drum is not sufficient, the heating of (or the heat transfer to) the film is changed, and the unevenness in the density of the image is enlarged as compared with that in the earlier art. Accordingly, the tight contact of the film F with the heated surface must be emphasized as compared with in the earlier art, and it is important to optimize the biasing force of the opposed rollers and the alignment between the heating drum and each opposed roller.
Further, when the number of opposed rollers is small in the opposed roller method, it is difficult that the film is tightly in contact with the drum at a curvature of the drum surface in the carrying direction. Particularly, a small volume of vacancy is formed between the drum and the opposed roller each time the film faces the opposed roller, and the unevenness in the density of the image can be easily formed.
In case of the use of the drum coated with fluororesin, it was found out by the experiment of the inventors that there is/are a steep change(s) in the distribution of temperatures in the neighborhood of the surface of the drum, as compared with the case of the use of the drum coated with silicon rubber. Therefore, when the contact of the film with the drum is not sufficient, the heating of (or the heat transfer to) the film is changed, and the unevenness in the density of the image is enlarged as compared with that in the earlier art. Accordingly, the tight contact of the film F with the heated surface must be emphasized as compared with in the earlier art, and it is important to optimize the biasing force of the opposed rollers and the alignment between the heating drum and each opposed roller. Further, in view of characteristics of the drum coated with fluororesin, it is required to optimize the number of opposed rollers.
In order to solve the above problem, a main object of the present invention is to provide a thermal development apparatus, in which photothermographic imaging material is stably carried while being tightly in contact with a heating section, when the heating section has a smooth layer made of fluororesin or the like on its surface, and the unevenness in the density of an image, particularly, the unevenness in the density at a top of the photothermographic imaging material is prevented.
A subordinate object of the present invention is to provide a thermal development apparatus, in which photothermographic imaging material is tightly in contact with a heating section used to heat and develop the photothermographic imaging material while carrying the photothermographic imaging material, when the heating section has a smooth layer made of fluororesin or the like on its surface, and the unevenness in the density of an image is reduced.
In order to accomplish the above-mentioned main object, in accordance with the first aspect of the present invention, a thermal development apparatus comprises:
a heating section, which has at least a portion of its outer surface formed in an arc shape and has a smooth layer on outermost surface of the arc-shaped portion, for carrying photothermographic imaging material being in contact with the smooth layer on the arc-shaped portion while heating the photothermographic imaging material; and
a plurality of opposed rollers, arranged along a carrying path of the photothermographic imaging material carried by the smooth layer on the arc-shaped portion of the heating section, for pressing the photothermographic imaging material against the arc-shaped portion,
wherein following formula and relations
P=2xcfx80Rxcex1/360,
2r+3xe2x89xa7P greater than 2r, and
xcex2xe2x89xa660
are satisfied when R (mm) denotes a radius of the arc-shaped portion, r (mm) denotes a radius of the opposed rollers, xcex1 (degree) denotes an angle between lines respectively connecting a center of the arc-shaped portion and centers of the two opposed rollers adjacent to each other, P (mm) denotes a pitch of the opposed rollers, and xcex2 (degree) denotes a contact angle of the photothermographic imaging material to the opposed roller.
In the first aspect of the present invention, when the heating section (heating member) has the smooth layer (surface layer) made of fluororesin on the surface of the heating section, the photothermographic imaging material can be tightly in contact with the outer surface of the heating section and be carried while the photothermographic imaging material is pressed on the heating section between the opposed roller (pressing roller) and the heating section. The photothermographic imaging material can be stably carried, and the unevenness in the density of the image specifically on the top side of the material in the carrying direction can be prevented.
Preferably, the heating section comprises:
a base body;
an elastic layer arranged around the base body and made of an elastic member having thermal conductivity equal to or higher than 0.5 W/k and JIS-A stiffness ranging from 20 degrees to 70 degrees; and
the smooth layer formed on the outer surface of the elastic layer and coated with fluororesin.
Preferably, a nipping force of each opposed roller in pressing the photothermographic imaging material to the outer surface of the smooth layer of the heating section ranges from 0.06N/cm to 1N/cm.
Preferably, a thickness of the smooth layer of the heating section ranges from 10 xcexcm to 100 xcexcm.
Preferably, the opposed rollers are supported together by a supporting member, and a position of the supporting member is adjustable relatively to the arc-shaped portion of the heating section.
In this invention, the parallelism between the heating section and each opposed roller in the axial direction of the heating section formed in the arc shape can be appropriately adjusted. Accordingly, the photothermographic imaging material can be tightly and uniformly in contact with the outer surface of the heating section.
In order to accomplish the above-mentioned subordinate object, in accordance with the second aspect of the present invention, a thermal development apparatus comprises:
a heating section, having a predetermined curvature, for heating photothermographic imaging material; and
a plurality of opposed rollers arranged along an axial line of the heating section so as to press the photothermographic imaging material to the heating section, the photothermographic imaging material being developed while being carried between the heating section and each opposed roller,
wherein the heating section comprises:
a base body having the predetermined curvature;
an elastic layer arranged around the base body; and
a smooth layer arranged on an outer surface of the elastic layer,
and wherein parallelism between each opposed roller and the heating section is adjusted within a predetermined amount so that each departure of the opposed rollers from an outer surface of the heating section is kept equal to or lower than a predetermined value.
In the second aspect of the present invention, each opposed roller is arranged at a relative position to the heating section on condition that the parallelism between the opposed roller and the heating section is set so as to make the departure of the opposed roller from the outer surface (smooth layer) of the heating section be equal to or lower than a predetermined value. Accordingly, the photothermographic imaging material can be tightly in contact with the heating section, and the unevenness in the density of the image can be prevented.
Preferably, the smooth layer of the heating section is made of fluororesin.
In this invention, the deterioration of the elastic layer, for example, made of silicon rubber caused by gas released from the photothermographic imaging material in the developing of the film can be prevented. In case of the heating section having the smooth layer made of fluororesin, the tight in contact of the photothermographic imaging material with the heating section is especially required. Because the requirement for the parallelism is satisfied as described above, the unevenness in the density of the image can be prevented.
Preferably, a nipping force of each opposed roller in pressing the photothermographic imaging material to the heating section ranges from 0.06N/cm to 1N/cm.
In this invention, The nipping force can be controlled by adjusting the biasing force of a biasing force generating means for making the opposed roller press the photothermographic imaging material to the heating section. Accordingly, the photothermographic imaging material can be tightly in contact with the smooth layer of the heating section.
Preferably, a film thickness of the smooth layer ranges from 10 xcexcm to 100 xcexcm.
In this invention, when the film thickness of the smooth layer is equal to or larger than 10 xcexcm, the adverse influence of gas of the elastic layer placed under the smooth layer in the developing can be prevented. When the film thickness of the smooth layer is equal to or smaller than 100 xcexcm, the unevenness in the density of the image hardly occurs.
Preferably, the opposed rollers are supported together by a supporting member, and a position of the supporting member is adjustable relatively to the heating section.
In this invention, the parallelism between each opposed roller and the heating section (deviation of each opposed roller from the heating section) can be appropriately adjusted. Accordingly, the photothermographic imaging material can be tightly and uniformly in contact with the heating section.
The predetermined value of the departure is preferably equal to or lower than 10 xcexcm when a film thickness of the smooth layer is equal to 100 xcexcm. The predetermined value of the departure is preferably equal to or lower than 14 xcexcm when a film thickness of the smooth layer is equal to 50 xcexcm. The predetermined value of the departure is preferably equal to or lower than 18 xcexcm when a film thickness of the smooth layer is equal to 30 xcexcm.
In this invention, the unevenness in the density of the image can be reliably prevented.